@laptop, This appears to be a bug in codeignitor. However,it also appears as if you alone are seeing this error, We are not seeing other reports of the problem.
Given that, the only way to debug this might be to catch it as it happens. I would be happy to assist but this will mean providing access to your server (for example FTP or SSH access).
Please feel free to PM me here or on slack if you wish to proceed with this course of action.